With many victims in the hospital reported to be in critical condition, the death toll is likely to rise.

Calling the attack “brutal murder”, the president said: “We stand with the people of Orlando, who have endured a terrible attack on their city. This is an especially heartbreaking day for all of our friends and fellow Americans who are lesbian, gay, transgender and bisexual.”

He added: “We know enough to say this was an act of terror and an act of hate.”

Officials described the shooting as an “act of domestic terrorism”, and said there were “suggestions” that the gunman “may have had leanings” toward a violent jihadist ideology.

The highest-casualty so-called “active shooter” incident before Sunday was the 2012 mass shooting at a movie theater in Aurora, Colorado, which had a total of 70 casualties – 12 people killed and 58 injured – according to a 2014 FBI study of shooting incidents.

The San Bernardino attack last year, a terror attack in which a married couple opened fire on a holiday party staged for the husband’s coworkers, left 14 people killed and 21 wounded.

The April 2013 Boston Marathon bombings, carried out with bombs made with pressure cookers, left three people dead and more than 260 injured.

In an international context, the shooting claimed fewer victims than the Paris terror attacks last November, which left 130 people dead, including 89 killed in a shooting massacre during a concert at the Bataclan theater.

In July 2011, a mass shooting in Norway also claimed more than 130 total casualties, many of them teenagers. In that shooting, which targeted an island summer camp, 69 people were killed and 66 wounded. The shooter, Anders Breivik, said he intended to oppose an “invasion of Muslims” into Europe and to attack supporters of multiculturalism. The shootings followed a bomb attack on Norway’s capital that left eight dead.

American mass shootings with no links to terrorism have seen a high number of people killed and injured, but none previously with such casualty figures, according to the 2014 FBI study.

A school shooting at Virginia Tech University in 2007 left 32 people dead. A school shooting at Sandy Hook Elementary School in Newtown, Connecticut, left 26 people dead, 20 of them first-grade students.

A separate Mother Jones analysis of public mass shootings since 1982 also includes no incidents with more than 100 total casualties, and no incident with more than 33 people shot to death.

Some prominent mass shootings before 1982 left fewer Americans dead than Sunday’s nightclub attack. In August 1966, a former marine armed with a number of guns climbed to the top of of a tower at the University of Texas at Austin and fired down on students below for more than an hour and a half, leaving 16 people dead and 31 people wounded.

In 1949, a disturbed young man walked through his Camden, New Jersey, neighborhood with a pistol and shot local residents. Thirteen people were killed in this “Walk of Death”, one of the country’s earliest high-profile mass shootings.

The 2014 FBI study analyzed “active shooter” incidents in the US between 2000 and 2013. These were public shootings that involved “an individual actively engaged in killing or attempting to kill people in a confined and populated area”, in which law enforcement and civilians had a chance to intervene and affect the outcome of the incidents. Gang or drug-related shootings were not included in the count.

Omar Mateen identified as shooter in Orlando nightclub attack

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There were 160 such incidents in the US between 2000 and 2013, the FBI found, with 486 people killed and 557 people wounded. Incidents happened in 40 of the 50 states. The majority of the incidents ended before police arrived, and 40% of the shooters committed suicide, many at the scene of the crime. Almost all of the shooters worked alone.

The frequency of such incidents has appeared to increase in recent years, the FBI found, from an average of 6.4 incidents each year in the first seven years of the study to an average of 16.4 incidents a year during the last seven.